Automatic coffee brewing apparatus are well known where heated water is sprayed into a brew cone and then drips down into a decanter which rests upon a heating element for keeping the coffee hot. In such prior art apparatus, the water is typically maintained in a reservoir at the temperature required for brewing coffee, generally between 180 and 200.degree. F. This heated water is forced out of the reservoir by the introduction of a like quantity of cold water into the reservoir. The cold water is usually transported from a spigot or bottled water dispenser in the same or a similar decanter as that into which the brewed coffee will drip. The cold water must be manually transported from its source and poured into the coffee brewing apparatus.
Maintaining the elevated temperature of the water stored within the reservoir causes several problems. It requires the constant heating of the reservoir and consequently the constant consumption of electrical energy. Also, maintaining water in a reservoir in a heated condition causes lime and scale to build up therein. The lime and scale are subject to occasional flaking, or breaking off. It then travels with the water into the brew cone, where it affects the taste of the coffee brewed therefrom.
Prior art coffee brewing apparatus are also known which do not store water, but rather are plumbed into either the building water supply or a bottled water dispenser and which utilize a timer controlled solenoid valve to dispense the correct volume of water during the brewing process.
The use of a timer to control the volume of water to be used during brewing has several disadvantages. Timers commonly used in such applications are sensitive to line power fluctuations. The use of another device or appliance on the same electrical circuit as the coffee brewing apparatus, during the time in which the coffee brewing apparatus' timer is being used to measure the volume of water to be used in the brewing process, can result in a line voltage drop sufficient to slow the timer down. This can significantly increase the volume of water delivered. This results in inconsistency in the amount of water used in brewing and therefore also results in inconsistency in the taste of the coffee so brewed.
Timers used in prior art plumbed coffee brewing apparatus are also particularly sensitive to the temperature of the water being metered by the solenoid valve. Since warmer water has a lower density, less of it by weight will be metered into the brewing cone than would be the case with cooler water. Therefore, the amount of water actually used in the brewing process is dependent upon the consistency of the temperature at which the water is delivered to the coffee brewing apparatus.
As such, although the prior art has recognized the problems of having to manually refill the reservoir for each decanter brewed and of being unable to provide a consistently better tasting brew of coffee, the proposed solutions have to date been ineffective in providing a satisfactory remedy.